linux-kernel - [PATCH RT 2/2] net: gianfar: do not try to cleanup TX packets if they are not done

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Message-Id: <1396004220-5711-2-git-send-email-bigeasy@linutronix.de>
Date:	Fri, 28 Mar 2014 11:57:00 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	linux-rt-users@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH RT 2/2] net: gianfar: do not try to cleanup TX packets if they are not done

What I observe is that the TX queue is not empty and does not make any
progress. gfar_clean_tx_ring() does not clean up the packet because it
is not completed yet.
The root cause is that the DMA engine did not start yet (it was
preempted before doing so) and that dumb loop, loops until that packet
is gone.
This is broken since c233cf4 ("gianfar: Fix tx napi polling").

What remains are spurious interrupts if CPU0 cleans up TX packages and
CPU1 returns with IRQ_NONE.

Cc: stable-rt@...r.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 drivers/net/ethernet/freescale/gianfar.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/freescale/gianfar.c b/drivers/net/ethernet/freescale/gianfar.c
index 8f1afda..091945c 100644
--- a/drivers/net/ethernet/freescale/gianfar.c
+++ b/drivers/net/ethernet/freescale/gianfar.c
@@ -134,7 +134,6 @@ static int gfar_poll_sq(struct napi_struct *napi, int budget);
 static void gfar_netpoll(struct net_device *dev);
 #endif
 int gfar_clean_rx_ring(struct gfar_priv_rx_q *rx_queue, int rx_work_limit);
-static void gfar_clean_tx_ring(struct gfar_priv_tx_q *tx_queue);
 static void gfar_process_frame(struct net_device *dev, struct sk_buff *skb,
 			       int amount_pull, struct napi_struct *napi);
 void gfar_halt(struct net_device *dev);
@@ -2516,7 +2515,7 @@ static void gfar_align_skb(struct sk_buff *skb)
 }
 
 /* Interrupt Handler for Transmit complete */
-static void gfar_clean_tx_ring(struct gfar_priv_tx_q *tx_queue)
+static int gfar_clean_tx_ring(struct gfar_priv_tx_q *tx_queue)
 {
 	struct net_device *dev = tx_queue->dev;
 	struct netdev_queue *txq;
@@ -2939,10 +2938,14 @@ static int gfar_poll(struct napi_struct *napi, int budget)
 			tx_queue = priv->tx_queue[i];
 			/* run Tx cleanup to completion */
 			if (tx_queue->tx_skbuff[tx_queue->skb_dirtytx]) {
-				gfar_clean_tx_ring(tx_queue);
-				has_tx_work = 1;
+				int ret;
+
+				ret = gfar_clean_tx_ring(tx_queue);
+				if (ret)
+					has_tx_work++;
 			}
 		}
+		work_done += has_tx_work;
 
 		for_each_set_bit(i, &gfargrp->rx_bit_map, priv->num_rx_queues) {
 			/* skip queue if not active */
-- 
1.9.1

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